Electromagnetic valves are often used in applications that require precise control over a flow of fluid. An electromagnetic control valve typically includes a solenoid that is connected to a valve element, such as, for example, a poppet valve. The solenoid may be energized to move the valve element into and out of engagement with a valve seat to thereby regulate the flow of fluid through the valve. The electromagnetic properties of the solenoid may allow precise control over the position of the valve element relative to the valve seat and, thus, the flow of fluid through the valve. Accordingly, these types of control valves are well suited for use in applications that require precise control over the amount and/or timing of a flow of fluid.
For example, a fuel injector for an internal combustion engine may include an electromagnetic control valve that governs a fuel injection event. In one type of fuel injection system, the control valve is placed in fluid connection with a chamber in a fuel injector body. A cam is used to move a piston in the fuel injector body to exert a force on fuel provided to the chamber. When the control valve is open, the force of the piston acts to move fuel from the chamber through the control valve. Closing the control valve prevents fuel from escaping the chamber and allows the force of the piston to increase the pressure of the fuel. When the fuel reaches an injection pressure, a nozzle valve opens to inject the fuel into a combustion chamber. The fuel injection ends when the control valve opens to thereby allow fuel to escape from the chamber.
To precisely control the fuel injection event, the control valve should move quickly between the open and closed positions. Due to the high pressure of the fuel, the valve element of the control valve may experience significant resistance when moving out of engagement with the valve seat. To quickly overcome the resistance to opening, the control valve may include a device to assist in the opening of the valve.
An example of a device for assisting in the opening of the valve is described in U.S. Pat. No. 6,029,682 to Lewis et al. The described device includes a heavy return spring that is compressed when a solenoid moves the valve element into engagement with the valve seat. When the solenoid is de-energized, the heavy return spring acts to move a coupling member into contact with the valve element to assist in the opening of the control valve. However, after the connecting member impacts the valve element, only a timing spring with a lighter force acts on the valve element to continue moving the valve element to open the control valve.
Typically the force of the timing spring is significantly less than the force of the return spring, which allows the valve to be closed quickly. However, when the valve is opening, forces exerted by the pressurized fuel may overcome the force of the timing spring. This may temporarily delay full opening of the valve. Any delay in the opening of the control valve may cause an undesirable pressure fluctuation or pressure “shelf” in the fuel injection pressure. Any delay in the opening of the control valve may, therefore, result in an unpredictable fuel injection event, which may impact the operation of the engine.
The electromagnetic control valve of the present invention solves one or more of the problems set forth above.